1. Field of the Invention
The present invention relates to clamps and clamping apparatus in general and in particular to an improved clamp for use with automotive frame straightening machines.
2. Background of the Invention
Automobile frame straightening machines are used in the automobile repair and restoration industry to straighten and re-align damaged automobile frames. A typical frame straightening machine or "rack" may include a base frame for holding and securing the automobile to the rack, along with several hydraulic jacks for pulling the damaged frame back into alignment. Generally speaking, a person seeking to repair a damaged frame will first secure the automobile frame to anchor points on the rack and then connect one or more of the hydraulic jacks to certain strategic parts of the frame, so than when the hydraulic jacks are actuated, they will pull on the frame and bend it back into alignment. Because such frame racks are designed to be used on a wide variety of cars and trucks, the hydraulic jacks are usually permanently mounted to the frame straightening rack and are typically connected to the automobile frame by chains or cables that are in turn connected to individual clamps that have been secured to the frame.
The above-described frame straightening procedure is relatively straightforward for vehicles having the older body-on-frame type of construction, because the frames of such vehicles are generally made from heavy gage steel and are quite strong. Therefore, it is relatively easy to affix the clamps to any point on the frame without risk of locally crushing or damaging the frame. However, the frame straightening procedure is somewhat more difficult for automobiles having the newer type unibody construction. Essentially, automobiles having unibody construction rely on the body panels themselves to carry the majority of the structural loads and use only relatively light stiffener assemblies to carry and distribute to the body panels more concentrated loads. Most unibody automobiles will also have relatively heavy subframe assemblies to carry and distribute to the body stiffeners heavily concentrated loads, such as those imposed by the engine, transmission, and suspension assemblies. The relatively lightweight construction of unibody automobiles, therefore, makes it considerably more difficult to affix the currently available clamps to portions of the body or lightweight stiffener assemblies without deforming, or even crushing, the unibody structure.
While numerous kinds of clamps have been developed in an effort to reduce the chances of damaging such unibody structures, they cannot always be clamped to those portions of the structure that would maximize the leverage applied to the unibody structure by the hydraulic jacks. As a result, it is often necessary to resort to several separate frame straightening operations with the clamp at separate locations before the frame can be completely re-aligned. For example, while a typical light frame or stiffener assembly for a unibody automobile has a square or rectangular cross-section, most body clamps currently available can only clamp a single wall of the square "tube" stiffener. Consequently, if a sideways pulling force is exerted on the clamp by the hydraulic jack, the clamp may bend or even tear the side wall of the stiffener member, causing yet more damage that will need to be repaired.
Consequently, there is a need for an improved clamp for automotive frame machines that can simultaneously grip both side walls of a square or rectangular frame stiffener or "tube" to allow greater side forces to be exerted on the member without risking substantial deformation and without the need to resort to multiple pulling operations. Ideally, such a clamp should be "self-energizing," i.e., the clamping force should increase in relation to the pulling force, to reduce the likelihood that the clamp will slip off under heavy pulling loads. Finally, the clamp should allow a second hydraulic jack to be connected to it to further increase the side pulling force that can be exerted on the frame, thereby reducing the number of separate pulling operations needed to straighten the frame. Until this invention, no such clamp existed.